Chitosan-BODIPY fluorescent composite materials for photodynamical antibacterial and therapy

Chitosan-based fluorescent copolymers containing borodipyrromethene (BODIPY) were synthesized and investigated. In this work, fluorescent compound (BOD-4) containing -C ≡ CH was synthesized firstly. Subsequently, chitosan (CS)-based polymer CS-I was obtained through the -NH₂/-C ≡ C click reaction between BOD-4 and CS. Thirdly, CS-Py was prepared via Suzuki reaction between CS-I and pyridine. Finally, the synthesis of macromolecular photosensitizers, i.e. CS-Me and CS-Bn, was achieved by pyridinium salt formation. CS-Me and CS-Bn could produce reactive oxygen species (ROS) when exposed to white light, demonstrating superior light utilization efficiency. This strategy not only utilizes the photodynamic ability of photosensitizing molecules but also takes advantage of chitosan's biocompatibility and antibacterial efficacy. The photodynamic antimicrobial activities of the macromolecular photosensitizers have been tested against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). CS-Me and CS-Bn exhibited not only the inherent antibacterial properties but also photodynamic capabilities, which significantly enhance their antibacterial effectiveness. Under white light irradiation, bacteria can be effectively eradicated. When made into a film by loading CS-Me and CS-Bn onto transparent band-aid, excellent photodynamic antibacterial properties were obtained. CS-based photosensitizers maintain the biocompatibility and antibacterial properties of CS. In addition, they expand the scope of chitosan's application in photodynamic therapy (PDT) as well.